The present invention relates to an etching system and an etching method for dry-etching a semiconductor film and an insulating film.
Dry etching is essential for the production of highly integrated semiconductor integrated circuits and there are etching methods and etching systems utilizing reactive ion etching (RIE), magnetron enhanced RIE, electron cyclotron resonance (ECR) and the like.
FIG. 1 is a schematic diagram showing the principle of the magnetron enhanced RIE. Reactive gas 3 is fed into a vacuum container 1 via a gas flow controller 2 and is maintained at an adequate pressure by an exhaust flow control valve 4 and an exhaust system 5. An anode 6 and a cathode 7 are provided within the vacuum container 1. The cathode 7 also plays a role of a substrate table for supporting a substrate 8. The cathode 7 is connected to an RF generator 10 via a matching device 9 to cause RF discharge between the anode 6 and the cathode 7. Electromagnets 11 having different phases and opposing each other are disposed on the outside of the vacuum container 1 to facilitate the discharge within high vacuum.
While the etching method and etching system utilizing the magnetron enhanced RIE and electron cyclotron resonance have had no problem if the substrate has a size of about 6 inches in diameter or 6 inches square, the magnetron enhanced RIE has had a problem for a substrate having a size of 8, 10, 12 inches or more that a so-called bank of electrons is brought about, not effecting the original magnetron discharge that electrons drift and return. Accordingly, it becomes difficult to uniformalize the plasma density across the whole substrate and a bias of the plasma density is brought about. Depending on the bias, a specimen is often partially destroyed by ion damage or the like in an extreme case and a thin gate oxide film is likely to be damaged in particular. The ECR also has had a problem that the size and weight of the system cannot but be increased when substrates become large because a magnetic coil for ECR condition is used. Further, because the gas cannot be agitated within the plasma discharge and because the flow of the gas fed/exhausted into/from the plasma discharge must be controlled in high precision, a marked high precision gas feeding/exhausting method has been required, thus complicating and increasing the size of the system.
The present invention provides an etching method, for improving an uniformity of plasma density across the whole surface of a substrate, for enabling an uniform etching even for a substrate of 8 inches or more and for reducing damages of a substrate caused by a bias of plasma, and a configuration which allows a size and weight of a system which realizes the above method to be reduced in an RIE type etching system by providing electrodes for applying an electric field in parallel with the surface of the substrate, beside electrodes disposed so as to apply an electric field vertically to the surface of the substrate, and by not only drifting electrons/ions within the plasma in the direction parallel with the surface of the substrate but also by agitating only electrons or both electrons and ions by utilizing a phenomenon that although both electrons and ions move following a low frequency electric field when it is applied in parallel with the surface of the substrate, electrons can follow an RF electric field, but not ions, when it is applied in parallel with the surface of the substrate.
The plurality of electrodes disposed vertically to the surface of the substrate are connected with function generators, amplifiers for amplifying frequency generated by the function generators and a phase controller for controlling a phase of the function generator connected to the other electrode. An activation of reactive gas may be promoted, a plasma density may be uniformalized and an etching rate and etching uniformity may be improved by providing two sets of parallel plate type electrodes orthogonally in case of four electrodes for example and by applying an RF electric field having a Lissajous waveform from the two sets of the electrodes and by agitating mainly electrons. In case when there are six electrodes, an activation of reactive gas may be promoted, a plasma density may be uniformalized and an etching rate and etching uniformity may be improved by disposing the electrodes hexagonally, by applying an RF electric field between the set of electrodes opposing each other, by applying a low frequency electric field whose phase is shifted to the other four electrodes to move electrons by the RF electric field in the direction parallel to the surface of the substrate and to move positive and negative ions by the low frequency electric field in the direction parallel to the surface of the substrate to agitate the electrons and ions. Any number of the electrodes for applying the agitating electric field in the direction parallel to the surface of the substrate may be used so long as it is more than two in theory. It is a matter of course that the number may be an even or odd number. Further, the present invention allows a small and light-weight system to be constructed without requiring a magnetic coil like the ECR.
Further, an activation of reactive gas may be promoted more effectively, a plasma density may be uniformalized and an etching rate and etching uniformity may be improved because a force for accelerating positive ions in the direction vertical to the surface of the substrate by Lorentz""s force acts by applying a magnetic field in parallel with the surface of the substrate on the outside of the electrodes for applying the electric field in parallel to the surface of the substrate for agitating electrons and ions, beside accelerating positive ions in the direction vertical to the surface of the substrate by an ion sheath. The effect becomes significant especially when the magnetic field is a rotary magnetic field and the electric field parallel to the surface of the substrate has a frequency and phase which are in synchronism with the rotation of the rotary magnetic field. The present invention requires no bulky and heavy magnetic coil like those used in the ECR condition, thus allowing a small and light-weight system to be constructed.
Further, because the present invention allows the same effect of agitating gas itself to be obtained without controlling a flow of the reactive gas on the surface of the substrate precisely like the known etching system by uniformalizing the plasma density by agitating ions and electrons by the electric field or the magnetic field or the electric field+the magnetic field, there is less limit on the gas feeding and exhausting methods. Therefore, when a pump which may be mounted upward, downward, horizontally or obliquely such as a magnetic levitation type turbo pump is used, it may be mounted at a location giving a high maintainability. Further, a so-called system down time which occurs when the system causes a failure or the like may be shortened considerably. Still more, concerning to feeding of gas, the present invention requires no complicated gas feeding structure in the anode or cathode like the prior art system. It is of course needless to say that it is preferable to control the feed and exhaust of the gas precisely.
The present invention may be readily applied to a known cluster type multi-chamber or a corridor type multi-chamber. When it is applied to the multi-chamber, it is particularly effective in a semiconductor manufacturing process in which cleanliness of an interface between films is important by providing an etching chamber, an ashing chamber and a film forming chamber as the reaction chambers in the system because a film may be etched in the etching chamber by using a resist patterned by photolithography as a mask, the resist may be removed in the ashing chamber and another film may be formed on the patterned film in the film forming chamber. An adhesiveness of another film formed on a film may be improved by sputter-cleaning the surface of the patterned film after ashing and before forming the other film. Still more, a defect such as a dangling bond may be terminated by performing hydrogen annealing with heat or plasma or heat+plasma to the patterned film after ashing and before forming another film and one having no so-called hydrogen shortness can be fabricated by forming a fine film such as a nitride film after that.
As described above, an activation of reactive gas may be promoted, a plasma density may be uniformalized and an etching rate and etching uniformity may be improved by etching with a plurality of electrodes for applying an electric field in parallel to the surface of the substrate or means for applying a magnetic field in parallel to the substrate, beside the electrodes for applying an electric field vertically to the surface of the substrate. Further, because the means is small and light-weight, it is possible to reduce the size of the system. Further, the present invention allows a system having a high maintainability and requiring no complicated structure to be constructed because the gas is agitated by the electric field or the electric field+magnetic field.
The specific nature of the present invention, as well as other objects, uses and advantages thereof, will clearly appear from the description and from the accompanying drawings.